Fluidized catalyst conversion processes, such as Fluidized Catalytic Cracking (“FCC”) and Oxygenate to Olefins conversion (“OTO”), typically involve contacting a liquid or vapor feed with flowing molecular sieve catalyst particles at elevated temperature. The catalyst is generally separated from the reaction effluent in a disengagement region, where the reaction product is conducted away for further processing while returning the separated catalyst to the process. While a substantial portion of the catalyst particles is separated from the product effluent some portion of the catalyst particles (generally fines) will be conducted away from the process with the effluent vapor. Since carbon deposits form on the molecular sieve catalyst during the desired reaction, all or a portion of the separated catalyst is typically conducted to a regenerating region where the carbon is removed by oxidation, thereby restoring at least a portion of the catalyst's activity. Catalyst continuously returned to the conversion process from the regenerator is conventionally called equilibrium catalyst, or “Ecat”. As is the case with reactor product effluent, a substantial portion of the catalyst particles can be separated from the regenerator's vapor effluent (“flue gas”), but a portion of the catalyst particles (generally fines) will generally be conducted away from the regenerator with the flue gas.
For a conventional OTO process carried out in a fluid bed reactor/regenerator system, the fresh and Ecat catalyst particles used in the process typically range in particle size from about 1 to about 200 micrometers. An average particle size is on the order of about 75 micrometers. In operation, catalyst attrition tends to produce catalyst fines, i.e., catalyst particle fragments generally less than 40 micrometers and more typically less than 20 micrometers in size (or average diameter when the fines are spherical or approximately spherical). Even though steps are taken to remove them, a portion of the fines are generally conducted away from the process with either the reactor effluent, the regenerator effluent, or both.
The reactor and regenerator effluent streams are high-temperature streams, and it is frequently desirable to cool these streams during processing using, e.g., conventional heat exchange equipment. The catalyst fines in the effluent can adhere to the heat transfer surfaces in the heat exchange equipment, which lead to heat exchanger fouling resulting in a loss in cooling efficiency. There is therefore a need for a process for removing catalyst fines foulant from the heat transfer surfaces in the reactor and regenerator effluent heat exchangers.